Introduction

I didn't set out to do planetary science. Hazards research dominated my work for a couple of decades. In the late 1990s, I did a project on how the Internet was being used to organize opposition to the Cassini-Huygens mission to Saturn because of the plutonium dioxide power sources and heating units on the spacecraft. In 2001, NASA invited me to present this work at a five-center teleconference. Discussion after the paper turned to how NASA could better manage risk communication for a proposed mission they expected to be controversial: the Mars Sample Return Lander.

I was asked to follow the already emerging opposition to the mission, which was organizing online over the use of radioisotope thermal generators and over the prospect of possibly bringing martian microörganisms to Earth and triggering an "Andromeda strain" pandemic. I agreed to do so and began to "bone up" on Mars to understand the mission before the then-planned 2008 launch date. As I got into the research on Mars, the mission itself was repeatedly delayed and then cancelled due to Bush's vision for human missions to the Moon and Mars. After a real struggle to absorb Mars research, I found myself without a project! Rather than forget it all, I developed a Geography of Mars class for CSULB. [ VIEWGRAPH ]

Since 1997, there have been ten successful missions to Mars out of fourteen sent. The result is huge amounts of data and images: There is a lot to do, and I hope to encourage geography students to consider helping out.

Acquiring a Mental Map of Mars

It is important to develop a mental map of Mars to place various people's work in its regional context. That is a bit challenging. Martian feature names are decided by the International Astronomical Union (IAU), and they have a particular system for assigning names. Names are generally linked to albedo features, areas of light and dark, that were first identified in the 19th century maps of Schiaparelli (1877) and Antoniadi (who extended Sciaparelli's toponymy).

There are certain standards for name assignment that vary with the scale of the feature being proposed for a name. Large craters are named for dead scientists and authors who made some contribution to Mars study (e.g., Antoniadi Crater). Small craters are named for towns and villages on Earth, such as Bonneville Crater examined by the Spirit Rover. Large "valles" are named for Mars in one of the languages of Earth, so Ma'adim Vallis comes from the Hebrew name for Mars and Kasei Valles are named for the Japanese name for Mars. Small valles are named for Earth rivers in classical or contemporary languages, such as Allegheny Vallis.

There is a whole new vocabulary to master. A valley is not called a valley, but a "vallis"; a mesa is called a "mensa"; a mountain is called a "mons." An area or region is called a "terra," while a plateau is a "planum" and a plain is a "planitia." This vocabulary is designed to forestall glib generalizations about the kinds of processes that can create one or another feature. A valley implies erosion, transportation, and deposition by running water, which could be a misleading parallel on another planet. Maybe there was running water, or maybe another fluid entirely was involved, such as lava or brines.

As you try to learn the regional organization of Mars, you might turn to the USGS 1:5,000,000 quadrangles. There are 30 of them, each with a number, such as MC-14 (Mars Chart 14) and a name associated with an albedo feature in the quadrangle, such as Amenthes Quadrangle. That quadrangle is named for Amenthes Planum, but it's not very evocative if you are unfamiliar with Amenthes Planum.

Google Mars débuted in 2009. You can type in a feature name and it will put a mark on the map locating it. Unfortunately, you can't point at a spot on Mars and find out what it's called or what region it falls in. Google Earth Mars is an interactive mapping program and, as with Google Mars, it lets you do a search by feature name and it'll take you there. But you still can't point to a feature or region and ask for its name.

A very helpful resource is the Gazetteer of Planetary Nomenclature by the IAU and the USGS. It allows you to pick from a list of feature types, which brings up an alphabetical list you can scroll through. So, for example, I picked "Chaos/chaoses" from the feature list and then, fron the alphabetical list, I could pick "Aram Chaos" and a map comes up showing the outlines of that feature on a background map that you can zoom into and out of and pan around in. You can also click on the plus sign to access a menu that lets you change the background map to help you visualize the location better.

Orders of Relief Taxonomy

[ VIEWGRAPH ] To create a regional framework for my class, which débuted in Spring 2007, I decided to create a nested system, based on the "orders of relief" scheme often seen in introductory physical geography and world regional geography textbooks. Each textbook has its own scheme, with anywhere from three to seven orders mentioned. Because of these disparities, I became interested in the intellectual history of the idea and found that it traced back to a 1916 article by Nevin Fenneman in the Annals of the Association of American Geographers, entitled, "The physiographic subdivision of the United States." The scheme in this article had three nested subdivisions:

• Physiographic divisions (e.g., the Atlantic Plain or the Pacific Mountain System)
• Geomorphic provinces (e.g., the Pacific Border Province within the Pacific Mountain System
• Sections (e.g., the California Coast Ranges within the Pacific Mountain System)

Textbook schemes have expanded upward and downward. Commonly the first order is the division of Earth into oceanic surfaces and continental ones. The second order is often comparable to Fenneman's physiographic province. The third order may comprise or be comparable to Fenneman's geomorphic province. If present, the fourth order may be roughly comparable to Fenneman's sections. There may be a fifth and even a sixth and seventh order.

The scheme I developed for Mars is a kind of two dimensional taxonomy. One dimension is spatial scale and the other is planetary conspicuousness. The result is a five orders of relief system. The spatial dimension is nested: The fifth order nests within the fourth order, which nests within the third order, which nests within, not the second order, but the first order. The second order is a series of large and conspicuous planetary features that, together with the first order, can be used as a framework within which to situate and refer to lower order features. So, for instance, Noachis Terra could be described as in the Southern Highlands (first order) between Argyre Planitia and Hellas Planitia (gigantic craters described as second order objects). Meridiani Planum (where the Opportunity rover still roams) could be described as lying within Arabia Terra (third order) east of Valles Marineris (second order) to the northeast of Argyre Planitia and northwest of Hellas Planitia (second order).

First Order of Relief

[ VIEWGRAPH ] The first order of relief comprises huge divisions of the martian surface, covering at least a quarter of the planet. There are two such divisions: the crustal dichotomy and the Tharsis Rise.

The crustal dichotomy is a conspicuous division of the planet into its badly cratered, mostly high elevation southern two thirds and the much smoother, generally low elevation northern third. The crust under the Southern Highlands averages about 58 km in thickness, while the crust under the Northern Lowlands is thinner, averaging about 32 km.

The Southern Highlands are visually dominated by a profusion of craters at a wide range of sizes. Some landscapes are nearly saturated with craters, such that any new crater would necessarily obliterate all traces of another, older crater. Depending on the spatial resolution of imagery, craters may be as tiny as 10 m across ... or as huge as 2,300 km across (Hellas Planitia). In some places, craters take on a very distinctive martian appearance, the rampart crater, with a conspicuous raised blanket of ejecta surrounding it, sort of a "wet splat" effect. These distinctive craters are found in high latitude areas where there is evidence of subsurface ice.

Another common feature in many areas of the Southern Highlands is something that looks like a small channel system. Some of these have a densely branched, dendritic pattern like many precipitation-fed stream networks in humid regions on Earth. Others show single main trunks with very few, quite short tributaries that end abruptly in a kind of alcove. These are similar in appearance to groundwater-fed stream systems seen on Earth in arid regions. Other potential signs of surface or groundwater include layering on the sides of cliffs and crater rims.

The Northern Lowlands convey an entirely different appearance. Most of the area north of the crustal dichotomy is low in elevation and much smoother in appearance, with very few craters and most of them small. These are clearly much younger surfaces, which have had less time to accumulate crater damage. Surfaces here are smooth or slightly hummocky and, in higher latitudes, it is common to find polygon patterned ground. On Earth, such polygons form above permafrost as soil water expands and freezes and then thaws. Larger rocks are squeezed toward the surface as smaller rocks and soil ooze under them. At the surface, they are squeezed into stripes and clusters, forming the polygonal patterning.

Water ice and is often evident on the surface in the form of small glaciers (which may be dust covered) and frost deposits. The presence of soil ice can create interesting patterns when a crater does hit the area, with the weaker ice-rich surface layers being blown into wide craters and the more resistant bedrock underneath generating smaller cratering, creating weird bull's eye craters. Water ice is evident above the surface, too, in clouds that form and sometimes organize themselves into systems that look like our own mid-latitude wave cyclones and even Arctic hurricanes. These are quite common in the Northern Hemisphere winter in the Northern Lowlands surrounding the North Polar Ice Cap.

Tharsis Rise is a massive volcanic province that covers over a quarter of the planet's surface, forming a huge "lump" positioned astride the crustal dichotomy, centered roughly around the equator.

First Order of Relief

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First Order of Relief

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References

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• Pike, Richard J. 1974. Why not an extraterrestrial geography? The Professional Geographer 26, 3: 258- 261.

• Rodrigue, Christine M. 2001. Internet media in technological risk amplification: Plutonium on board the Cassini-Huygens spacecraft. Risk: Health, Safety, and Environment 12, 3 & 4: 221- 254. Available at http://www.csulb.edu/~rodrigue/risk01.html

• Tyner (then Zink), Judith A. 1963. Lunar Cartography: 1610-162. Master's thesis, Department of Geography, University of California, Los Angeles.

• Tyner, Judith A. 1969. Early lunar cartography. Surveying and Mapping 12: 583-596.